Devices and methods for influencing combustion processes by electrical manners/elements are disclosed in numerous citations. The use of electrical manners/elements, in particular electrical fields and discharges, is aimed at improving the stability of the combustion process, reducing pollutant emissions and suppressing combustion chamber oscillations. Examples of these include WO 96/01394 A1 and DE 101 37 683 C2.
WO 96/01394 A1 describes electrode arrangements which, disposed in a combustion chamber in the area of the flame burning there, are subjected to voltages having a variable time profile and are intended to exert an influence so as to reduce the emissions of pollutant substances such as soot, carbon dioxide, unburned organic substances and nitrogen compounds.
Besides the aim of reducing pollutant emissions, the object of DE 101 37 683 C2 is also to improve the stability of the combustion and in particular to suppress thermo-acoustic emissions. The manners/elements employed to do this differ from those described in WO 96/01394 A1 in that the electrodes are fitted on that side of the combustion chamber remote from the flame.
A major advantage of influencing flames by electrical fields and discharges is that the method can be used for controlling combustion processes with no response time lag. This method requires the provision of sensors for registering the variables to be influenced.
Sensors for picking up various types of signals from flames are known in numerous embodiments. Relevant sensors in the present context are ones comprising electrodes, which are introduced into the flame or into proximity with the flame in order to measure electrical characteristics of the flame.
One example of these is given in U.S. Pat. No. 5,049,063 A, which describes an electrode extending into the flame tip, which is used to measure an ion current. An ionization electrode is also provided in DE 196 32 983 C2, which relates to a control device for a gas burner. In both documents, the signal generated by the probe is used in conjunction with suitable amplifiers and filters to advantageously control the combustion process, for example by influencing the admission of air or gas by way of a control valve. The probe itself here serves solely for the detection of flame characteristics and is itself not used for influencing the combustion process. EP 0 775 870 B1 furthermore discloses a device for damping thermo-acoustic oscillations, especially of a combustion chamber for a gas turbine with electrically influenceable combustion chamber, in which a pressure sensor installed in the combustion chamber registers pressure oscillations and generates a signal for an electrode in the combustion chamber, for the purpose of electronically controlling the flame.
A disadvantage of the conventional engineering is that the effect exerted on the combustion process is achieved via mechanical systems such as valves, which are subject to wear and have a reaction time, which may be too long, especially for controlling combustion chamber oscillations.